4 replies to this topic

[Techohead]

hello to everyone,
a few months ago i made a design for my own black powder rocket, using my own black powder fuel, bentonite plugs and i lathed a complex profile onto a set of tools for ramming. the first rocket i made this way was hugely successful, reaching over 100 meters in height. i replicated it, again and again. i was making 10 per week and enjoying the delights of the effects i could lift with them. when terror struck in the form of a pyrotechnic ban enforced by my family. i decided if i was not allowed to 'make' any pyrotechnics for a couple of months, i'd better make a few last rockets and use them sparingly. i made 15 rockets, fitted some with visco ignition, some with electric ignition, and i left them lying ontop of my dvd player for almost a month. tonight i finally removed 4 of them from the dvd player, fitted a header on one, and went out to light them. the first rocket, electrically lit, blew it's nozzle out immediately. i put it down to 'the electric igniter must have been jammed to tightly in the nozzle'. i lit a visco fuse lit rocket, in which nothing blocked the nozzle at all, and the same thing still happened. huge explosion, and the shell of the rocket would go about 10 meters high, then fall back down. i noticed a trange thign was happening. not only was the nozzle failing and blowing out, so was the end plug!

now in a rocket, pressure will accumulate until the weakest point fractures, and the pressure discharges. if the nozzle blew out, the pressure should have escaped out of the open ended rocket, but for it to then continue and also blow out the top plug, there must have been astronomical internal pressures. i lit a third and fourth rocket, and all the same.

so far my only theory is that over time the moisture in the air has caused the chemicals in the black powder to 'precipitate' together, creating a much faster burning black powder, even though the powder was already as fast as i could make it by milling. if any has any ideas i'm open to hear them. unfortunately the remaining 11 rockets are now just ground reports or something of the likes. but i need to find out how to prevent it ever happening again.

[marble]

Its simple, the extra heat and dryness caused the BP and clay nozzle to shrink and dry, the BP fuel cracks and the nozzle is weak and loose fitting thus resulting in a cato.

Edited by marble, 10 April 2008 - 11:26 AM.

[Techohead]

yeah that seems more logical than my crazy theory. and the rocket would have been subjected to slightly above average temperatures lying on top of a dvd player that is always in use. but i, and any other good pyro, cannot afford to have unreliablity, so how do you recomment the rockets are stored to ensure they stay in good condition? or will simply not putting them on top of electrical devices fix the problem?

[marble]

I don't have any experience here (I don't like storing things) I would imagine ramming / pressing the fuel and nozzle very well and keeping the rocket stored in a stable environment would vastly help.

[digger]

yeah that seems more logical than my crazy theory. and the rocket would have been subjected to slightly above average temperatures lying on top of a dvd player that is always in use. but i, and any other good pyro, cannot afford to have unreliablity, so how do you recomment the rockets are stored to ensure they stay in good condition? or will simply not putting them on top of electrical devices fix the problem?

Yep I would put it down to the bentonite clay shrinking (it is very susceptible to expansion/contraction due to moisture gain/loss).

If you continue to use bentonite first dry it in the oven at 200ºC then before it has cooled add about 10% paraffin wax and let it melt in. While it is still hot ensure the wax is evenly distributed in the clay. Hey presto moisture proof bentonite. I am working on a new nozzle mix at the mo that is much harder than straight bentonite, I will post the formula when I have finished testing.

As to the bp fuel just make sure it is dry when first pressing and it should pose no problems for storage (assuming that it is kept in a stable environment, such as a sealed plastic box).

Edited by digger, 10 April 2008 - 12:11 PM.